This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 2000-320024 filed on Oct. 19, 2000 and Japanese Application No. 2001-037073 filed on Feb. 14, 2001, the entire contents of both of which is incorporated herein by reference.
This invention generally relates to a vehicle motion control device for controls such as traction control and brake steering control. More particularly, the present invention pertains to a vehicle motion control device which includes a hydraulic pressure control valve device between an automatic hydraulic pressure generator for generating brake hydraulic pressure by actuating a vacuum booster irrespective of operation of a brake pedal and respective wheel cylinders for controlling the automatic hydraulic pressure generator and the hydraulic pressure control valve in accordance with the motion condition of the vehicle for performing automatic pressure control relative to the wheel cylinders.
A vehicle motion control device in which the vacuum booster is applied to the automatic pressure control for traction control includes a booster actuator for actuating the vacuum booster irrespective of brake pedal operation. The traction control is performed by controlling the booster actuator irrespective of the brake pedal operation. To actuate the booster actuator, it is known to use a device provided with a linear solenoid for providing an appropriate control in accordance with the vehicle motion condition.
Various types of vacuum boosters are known. Generally speaking, vacuum boosters include a housing having an interior divided into a constant pressure chamber and a variable pressure chamber by a movable wall. The movable wall is connected in a unitary manner to a power piston, and the constant pressure chamber is always in communication with an intake manifold of the engine so that negative pressure is introduced into the constant pressure chamber. The power piston includes a vacuum valve for establishing or interrupting communication between the constant pressure chamber and the variable pressure chamber, and an air valve for establishing or interrupting communication between the variable pressure chamber and the atmosphere. The power piston is connected to a master cylinder via a reaction disc and an output rod. In the vacuum booster constructed in the foregoing manner, a booster actuator for automatically actuating the vacuum booster is provided to perform the automatic pressure control.
Japanese Patent Laid-Open Publication No. H10-258716 discloses a brake hydraulic pressure control device for improving the response at starting of a spool type hydraulic pressure control valve which is provide with a linear solenoid that functions as a hydraulic pressure control valve. According to this published application, when a target hydraulic pressure becomes greater than a predetermined value, a maximum actuating electric current is provided to the linear solenoid for a predetermined time. It is also proposed to vary the time period to provide the maximum actuating electric current in accordance with the target hydraulic pressure.
As disclosed in the Japanese Patent Laid-Open Publication No. H10-258716, when the brake hydraulic pressure control is performed by the electric current control of the linear solenoid, the electric current is instantaneously increased immediately after energization to start the brake control at a stretch. Then, the electric current is dropped or reduced to the target current level. This is intended to avoid the delay of starting the control and to reduce the dispersion of the output. However, in the case of a linear solenoid of the booster actuator provided in the automatic hydraulic pressure generator for generating the brake hydraulic pressure by actuating the vacuum booster irrespective of the operation of the brake pedal, various problems occur at automatic hydraulic pressure control when the brake pedal is not operated.
When the vacuum booster is actuated by energizing the linear solenoid of the booster actuator when the brake pedal is not operated, the air valve in the vacuum booster is suddenly opened to introduce atmospheric air into the variable pressure chamber. This generates a loud operation noise. Simultaneously, the valve operation is transmitted to the vehicle body via the reaction disc, thus generating vibration noise. These noises cannot be ignored from the standpoint of desirable NV performance (i.e., noise and vibration performance), particularly when the brake pedal is not operated, it is necessary to reduce the noise as mich as possible. Likewise, the tapping noise generated when the actuation of the vacuum booster is released by the booster actuator also needs to be reduced.
To address the aforementioned problems, it is necessary to gradually energize the linear solenoid. However, the foregoing known vehicle motion control device is designed to control the energization of the linear solenoid by increasing the electric current at one stretch and then dropping to the target electric current, to thus reduce the time delay of the energization of the linear solenoid for starting the operation which derives from the characteristics of the linear solenoid. Thus, gradual energization of the linear solenoid is not taken into consideration in the known vehicle motion control device. In the known vehicle motion control device, in the meantime, the energization of the linear solenoid of the booster actuator is instantaneously cut off when the actuation of the vacuum booster by the booster actuator is released upon ending the control.
A need thus exists for a vehicle motion control device for actuating the vacuum booster by the booster actuator which reduces the noise derived or resulting from the operation of the vacuum booster when the brake pedal is not operated.
The present invention provides a vehicle motion control device which includes a variable pressure chamber, a constant pressure chamber, a plurality of wheel cylinders provided on respective wheels of a vehicle, an automatic hydraulic pressure generator for generating a brake hydraulic pressure irrespective of operation of a brake pedal, a hydraulic pressure control valve device provided between the automatic hydraulic pressure generator and the respective wheel cylinders for controlling a brake hydraulic pressure of respective wheel cylinders, and a controller for performing a vehicle motion control by controlling the automatic hydraulic pressure generator in accordance with the vehicle motion condition of the vehicle, by controlling the hydraulic pressure control valve device, and by performing the automatic pressure control at the wheel cylinders irrespective of the operation of the brake pedal. The automatic hydraulic pressure generator includes a linear solenoid, a vacuum booster operating at least in accordance with the operation of the brake pedal, and a booster actuator for actuating the vacuum booster by controlling the linear solenoid based on a predetermined target electric current irrespective of the operation of the brake pedal. The controller makes a determination to instantaneously increase the target electric current of the linear solenoid to an electric current value which corresponds to an electric value immediately before the vacuum booster starts the operation and which is lower than a maximum value of the target electric current of the linear solenoid, and to gradually increase the target electric current of the linear solenoid close to the maximum value of the target electric current when the brake pedal is not operated.
According to another aspect of the invention, the vehicle motion control device includes a variable pressure chamber, a constant pressure chamber, a plurality of wheel cylinders provided on respective wheels of a vehicle, an automatic hydraulic pressure generator for generating a brake hydraulic pressure irrespective of operation of a brake pedal, a hydraulic pressure control valve device provided between the automatic hydraulic pressure generator and the respective wheel cylinders for controlling a brake hydraulic pressure of respective wheel cylinders, and a controller for performing a vehicle motion control by controlling the automatic hydraulic pressure generator in accordance with the vehicle motion condition of the vehicle, by controlling the hydraulic pressure control valve device, and by performing the automatic pressure control at the wheel cylinders irrespective of the operation of the brake pedal. The automatic hydraulic pressure generator includes a linear solenoid, a vacuum booster operating at least in accordance with the operation of the brake pedal, and a booster actuator for actuating the vacuum booster by controlling the linear solenoid based on a predetermined target electric current irrespective of the operation of the brake pedal. The controller makes a determination to instantaneously decrease the target electric current of the linear solenoid from the actuated condition by the booster actuator to a termination target value which corresponds to an electric value immediately before stopping the actuation of the vacuum booster, and then to gradually decreases the target electric current of the linear solenoid until decreasing to approximately zero when the brake pedal is not operated.
According to a further aspect of the invention, the vehicle motion control device includes a variable pressure chamber, a constant pressure chamber, a plurality of wheel cylinders provided on respective wheels of a vehicle, an automatic hydraulic pressure generator for generating a brake hydraulic pressure irrespective of operation of a brake pedal, a hydraulic pressure control valve device provided between the automatic hydraulic pressure generator and the respective wheel cylinders for controlling a brake hydraulic pressure of respective wheel cylinders, and a controller for performing a vehicle motion control by controlling the automatic hydraulic pressure generator in accordance with the vehicle motion condition of the vehicle, by controlling the hydraulic pressure control valve device, and by performing the automatic pressure control at the wheel cylinders irrespective of the operation of the brake pedal. The automatic hydraulic pressure generator includes a linear solenoid, a vacuum booster operating at least in accordance with the operation of the brake pedal, and a booster actuator for actuating the vacuum booster by controlling the linear solenoid based on a predetermined target electric current irrespective of the operation of the brake pedal. The controller makes a determination to gradually decrease the target electric current of the linear solenoid from the actuated condition by the booster actuator until decreasing to approximately zero when the brake pedal is not operated.
According to still further aspect of the present invention, a vehicle motion control device includes a plurality of wheel cylinders provided on respective wheels of a vehicle, an automatic hydraulic pressure generator for generating a brake hydraulic pressure irrespective of operation of a brake pedal, a hydraulic pressure control valve device provided between the automatic hydraulic pressure generator and the respective wheel cylinders for controlling a brake hydraulic pressure of respective wheel cylinders, and a controller for performing a vehicle motion control by controlling the automatic hydraulic pressure generator in accordance with the vehicle motion condition of the vehicle, by controlling the hydraulic pressure control valve device, and by performing the automatic pressure control at the wheel cylinders irrespective of the operation of the brake pedal. The automatic hydraulic pressure generator includes a linear solenoid, a vacuum booster operating at least in accordance with the operation of the brake pedal, and a booster actuator for actuating the vacuum booster by controlling the linear solenoid based on a predetermined target electric current irrespective of the operation of the brake pedal. The controller makes a determination to instantaneously increase the target electric current of the linear solenoid to a starting target value which corresponds to an electric current value immediately before the vacuum booster starts the operation by the actuation of the booster actuator and which is less than the maximum value of the target electric current of the linear solenoid, and to gradually increase the target electric current approximately to the maximum value of the target electric current when the brake pedal is not operated and before the vehicle motion control starts.
The automatic pressure control when the brake pedal is not operated before the start of the vehicle motion control is referred to here as a pre-control.